In a typical lumber mill or planer mill, each board is oriented transversely on a lugged transfer moving laterally towards the trimmer. Typically, the lugs on the transfer are evenly spaced at precise intervals. The boards are passed through an electronic scanner which determines the shape of each board and sends the shape information to an optimizer. The optimizer in turn sends the information to a controller. The controller adjusts a positioning fence and activates saws above a trimmer saw deck to trim the board in an attempt to maximize lumber utilization. Typically saws are spaced one foot apart or conversely two feet apart, so that depending upon the particular mill setup and the physical defects of a board, two feet of each end of the board could potentially be trimmed and thus wasted if the trim target is missed, this results in considerable wastage of useful wood and loss of profits.
In order to minimize such wastage, board positioners were developed utilizing a plurality of parallel rollers, or ending rolls, which are driven in a direction at right angle to the transfer deck, thus moving the ends of the boards up to a positioning fence. When on the rollers, the boards are continually thrust laterally across the transfer deck, until the board is raised above the rollers by a plurality of lift skids to disengage the board from the rollers at a predetermined place. Such prior art devices have the disadvantage that when wet or icy boards are being ended, slippage of the boards can cause a jerking movement in a manner which will cause chattering and bouncing of the boards on the ending fence and when the lift skids lift the board at the predetermined ending position, inaccuracies result. As well, the lift skids are complex, each requiring an activation cylinder and there is an extra control system needed to raise each skid group in time with the lugged transfer chains along the length of the ending fence as needed and if applicable, extending along the stages of the ending fence.
Such devices suffer from the fact that tapered ends of boards abutting the positioning fence can be so structurally weak as to collapse or break when contacting (bouncing, chattering) and sliding along the fence. Because the board was scanned and optimized based on the inclusion of the tapered ends, if the end is broken off, the optimized lengthwise movement of the board can be overshot as the broken board is ended against the positioning fence, resulting in a board that is over trimmed.
It is therefore an object of the present invention to provide a board positioning device which can gently and accurately position selected boards for trimming at a higher rate of speed than prior art devices and without damage or collapse of the board's weak ends, so as to thus provide an improvement in accuracy for optimally trimming boards.
In another problem with most existing apparatus of the general type, the setting of each board in sequence limits the time available to reset the next piece, also as speeds increase, more stages are added to allow for greater ending. This results in a longer installed length, and is therefor more difficult to retrofit, in addition as mentioned a multiple number of lift skids, which attempt to hold the boards position after ending, are needed in most board positioners which adds to the number of moving parts and the controls needed to operate these lift skids are also increased.
It is therefor another object of the present invention to provide an apparatus that will not require additional space and to also eliminate the need for lift skids and the controls needed to operate the lift skids in sequence with the lugged transfer chains.